1. Field of the Invention
The invention relates generally to integrated circuits and more particularly to interconnecting individual devices of an integrated circuit.
2. Background Information
One direction in improving integrated circuit technology is to reduce the size of the components or devices on the integrated circuit chip, permitting an increased number of devices on the chip. The reduction in size of the devices of an integrated circuit chip requires reductions in the widths and thicknesses of the interconnections that connect the devices on the chip.
In general, the primary concerns of interconnection material is the material""s longevity and its resistivity. Typically, modern interconnections are made principally of aluminum or an aluminum alloy, such as an aluminum-copper (Alxe2x80x94Cu) alloy or aluminum-silicon (Alxe2x80x94Si) alloy.
In general, grain boundaries are formed by the aluminum crystals that make up the aluminum or aluminum alloy interconnection. At present, the xe2x80x9cmicronxe2x80x9d width and the xe2x80x9cangstromxe2x80x9d thickness of a typical interconnection has become so small that interactions between the current flowing through the interconnection and the grain boundaries between the aluminum crystals increasingly determine the limits in performance, reliability, and power consumption.
Where three grain boundaries meet, a triple point junction is formed. Such junctions are randomly dispersed throughout the interconnection and extend in a variety of directions that define potential inlet and outlet routes for displaced aluminum atoms during current flow. As electrical current flows through the interconnection, aluminum atoms are displaced the electrons. These displaced aluminum atoms accumulate in the grain boundaries that are downstream of the current and travel along the grain boundaries in the general direction of the current. At grain boundary junctions that have fewer upstream inlets than downstream outlets, a void may develop at that grain boundary junction in the interconnection over time as aluminum atoms erode from the junction.
FIG. 1 schematically illustrates an aluminum alloy interconnection and shows a number of junctions created by adjacent aluminum crystals. Interconnection 70 is formed, in this example, by a portion of aluminum crystal 72, a portion of aluminum crystal 74, a portion of aluminum crystal 76, a portion of aluminum crystal 78, and a portion of aluminum crystal 80. Grain boundary junction 82 is formed by the meeting of inlet grain boundary 84, outlet grain boundary 86, and outlet grain boundary 88, the designation of inlet and outlet being dictated by the indicated direction of the flow of electrons. With one upstream inlet and two downstream outlets, more aluminum atoms can be expected to leave junction 82 through the two downstream outlets 86 and 88 than are supplied into junction 82 through the one upstream inlet 82. With more aluminum atoms being removed from junction 82 within interconnection 70 than are being supplied to junction 82 from its upstream source, here inlet grain boundary 84, void 90 eventually will develop in interconnection 70 at junction 82.
The movement of aluminum atoms within an aluminum interconnection is known as electromigration and the time it takes for a void to develop into an open circuit in the interconnection may be described as the electromigration lifetime. One way to increase performance, reliability, and power consumption of integrated circuit interconnections is by improving the electromigration lifetime.
Several techniques have been developed to improve the electromigration lifetime of an interconnection. These techniques include improved texture, interlayers to limit void size, and interconnections of multiple layers of material such as a pure aluminum layer as well as different layers formed from aluminum alloys.
A second concern of interconnections is resistivity. U.S. Pat. No. 4,673,623, demonstrated that an alloy of aluminum, silicon, and titanium (Alxe2x80x94Sixe2x80x94Ti) provides hillock-free, dry-etchable, low resistivity electromigration resistant interconnections. Prior to the Alxe2x80x94Sixe2x80x94Ti alloy, interconnections of both aluminum-silicon (Alxe2x80x94Si) and aluminum-silicon-copper (Alxe2x80x94Sixe2x80x94Cu) were utilized. Although adding copper to aluminum-silicon improved the performance of the interconnection, the replacement of copper with titanium dramatically improved the performance of the interconnection by reducing the resistivity over an Alxe2x80x94Sixe2x80x94Cu interconnection.
What is needed is an electrical interconnection and an interconnection system with improved performance and reliability.
An interconnection of an aluminum-copper-Group IVA metal alloy is disclosed.